The present invention relates to a method for producing 2,3-dichloro-1-propanol (hereinafter, sometimes abbreviated as xe2x80x9c2,3-DCHxe2x80x9d), which is an intermediate for the production of epichlorohydrin used as a solvent, a raw material for producing epoxy resin, a raw material for producing synthetic rubbers, a stabilizer for chlorinated rubber raw material and the like and to a method for producing epichlorohydrin (hereinafter, sometimes abbreviated as xe2x80x9cECHxe2x80x9d) from 2,3-DCH. The invention relates to a method for producing 2,3-dichloro-1-propanol by reacting allyl alcohol with chlorine in a hydrochloric acid solution.
Many proposals have been made on the production method for producing 2,3-dichloro-1-propanol (2,3-DCH) by chlorinating allyl alcohol with chlorine in a hydrochloric acid solution. In particular, it has been known that reaction of allyl alcohol with chlorine in a high concentration hydrochloric acid solution can produce 2,3-DCH in high yields (Japanese Patent Application Laid-open Nos. 59-128340, 59-128341, and 3-74342, etc.)
As an industrially useful continuous production method for 2,3-DCH, for example, Japanese Patent Application Laid-open Nos. 59-128340, 60-258171 (U.S. Pat. No. 4,634,784), and 3-74342, etc. disclose methods for the production of 2,3-DCH by introducing a solution obtained by chlorination of allyl alcohol in a hydrochloric acid solution into a degassing tower and heating the solution to release hydrogen chloride, followed by recovering the hydrogen chloride and sending it to the reactor. As for the proportions between allyl alcohol and chlorine used in these methods, Japanese Patent Application Laid-open No. 3-74342 describes supply of an excessive amount of chlorine in a range of 10 mol % or less to allyl alcohol, and Japanese Patent Application Laid-open No. 59-128340 describes that the amount of chlorine of about 1.05 mol or less per mol of allyl alcohol is sufficient.
However, in the continuous method for the production of 2,3-DCH by introducing a solution obtained by chlorination of allyl alcohol in a hydrochloric acid solution in a degassing tower and heating the solution to release hydrogen chloride, followed by recovering the hydrogen chloride and sending it to the reactor, there has been a problem in that the continued supply of chlorine in amounts more than stoichiometric proportion with respect to allyl alcohol results not only in a loss of excessively supplied chlorine but also in a reduction in the partial pressure of gas phase hydrogen chloride in the hydrogen chloride absorber and/or reactor, which in turn causes a reduction in the yield of 2,3-DCH. Conversely, the continued supply of allyl alcohol in amounts more than stoichiometric proportion with respect to chlorine will not only cause a problem of a loss of unreacted allyl alcohol but also invite clogging of the heater of the degassing tower due to accumulation of the polymer, so that the operation cannot be continued in a stable manner for a long time.
Furthermore, Japanese Patent Application Laid-open No. 3-74342 describes that the concentration of allyl alcohol in the reaction mixture that is continuously taken out of the system should be substantially zero. However, it contains no specific description as to how to make the concentration of allyl alcohol to zero.
Therefore, an object of the present invention is to provide a continuous method for the production of 2,3-DCH by introducing a solution obtained by chlorination of allyl alcohol in a hydrochloric acid solution into a degassing tower and heating the solution to release hydrogen chloride, followed by recovering the hydrogen chloride and sending it to the reactor, in which the concentration of allyl alcohol remaining in the reaction mixture introduced in the degassing tower is made substantially zero so that 2,3-DCH and epichlorohydrin can be continuously produced in high yields and in a stable manner for a long time.
Under the circumstance, extensive studies have been made and as a result, it has now been found that in a continuous method for the production of 2,3-DCH by introducing a solution obtained by chlorination of allyl alcohol in a hydrochloric acid solution into a degassing tower and heating it to release hydrogen chloride, followed by recovering the hydrogen chloride and sending it to the reactor, in order to make the concentration of allyl alcohol remaining in the reaction mixture introduced in the degassing tower substantially zero and continuously obtain 2,3-dichloro-1-propanol in high yields, it is necessary to control the concentration of chlorine dissolved in the reaction mixture to be introduced in the degassing tower to a specified concentration or less and/or to control the partial pressure of chlorine gas present in the gas phase section of the reactor immediately before the degassing tower to a specified partial pressure or less. It is further recognized that it is important to arrange an automatic analyzer for measuring the chlorine concentration in a solution at the outlet of the reactor immediately before the degassing tower and/or the concentration (partial pressure) of chlorine gas present in the gas phase section of the reactor as means for controlling the concentration of chlorine dissolved in the reaction mixture in the reactor immediately before the degassing tower and/or the partial pressure of the gas phase section of the reactor immediately before the degassing tower within a specified range and control the flow rate of chlorine gas to be introduced into the reactor immediately before the degassing tower in accordance with the reading of the analyzer. Thus, the present invention has been accomplished.
That is, the present invention provides methods for producing 2,3-dichloro-1-propanol and methods for producing epichlorohydrin as described below:
1) A method for producing 2,3-dichloro-1-propanol by introducing a solution containing 2,3-dichloro-1-propanol obtained by chlorination of allyl alcohol in a hydrochloric acid solution into a degassing tower to release hydrogen chloride, returning the hydrogen chloride to a reactor for the chlorination, and obtaining 2,3-dichloro-1-propanol from the remaining solution, characterized in that the method comprises maintaining the concentration of chlorine dissolved in the solution at an outlet of the reactor immediately before introduction to the degassing tower to 0.015 g/ml or less.
2) A method for producing 2,3-dichloro-1-propanol by introducing a solution containing 2,3-dichloro-1-propanol obtained by chlorination of allyl alcohol in a hydrochloric acid solution into a degassing tower to release hydrogen chloride, returning the hydrogen chloride to a reactor for the chlorination, and obtaining 2,3-dichloro-1-propanol from the remaining solution as described in 1) above, characterized in that the method comprises arranging in the reactor immediately before degassing tower an analyzer for monitoring the concentration of chlorine dissolved in the solution at an outlet of the reactor and controlling the flow rate of chlorine gas to be introduced into the reactor so that the concentration of chlorine can be maintained at 0.015 g/ml or less.
3) A method for producing 2,3-dichloro-1-propanol by introducing a solution containing 2,3-dichloro-1-propanol obtained by chlorination of allyl alcohol in a hydrochloric acid solution into a degassing tower to release hydrogen chloride, returning the hydrogen chloride to a reactor for the chlorination, and obtaining 2,3-dichloro-1-propanol from the remaining solution, characterized in that the method comprises maintaining the partial pressure of chlorine in a gas phase section in the reactor immediately before the degassing tower to 0.08 MPa (absolute pressure) or less.
4) A method for producing 2,3-dichloro-1-propanol by introducing a solution containing 2,3-dichloro-1-propanol obtained by chlorination of allyl alcohol in a hydrochloric acid solution into a degassing tower to release hydrogen chloride, returning the hydrogen chloride to a reactor for the chlorination, and obtaining 2,3-dichloro-1-propanol from the remaining solution as described in 3) above, characterized in that the method comprises arranging in the reactor immediately before degassing tower an analyzer for monitoring the concentration of chlorine gas in the gas phase section of the reactor and controlling the flow rate of chlorine gas to be introduced into the reactor so that the partial pressure of chlorine gas can be maintained 0.08 MPa (absolute pressure) or less.
5) A method for producing 2,3-dichloro-1-propanol as described in any one of 1) to 4) above, wherein a hydrochloric acid aqueous solution containing 40 to 75 mass % of hydrogen chloride as HCl/(H2O+HCl) is used.
6) A method for producing 2,3-dichloro-1-propanol as described in any one of 1) to 4) above, wherein the chlorination reaction of allyl alcohol is performed at a temperature of xe2x88x9230 to +20xc2x0 C.
7) A method for producing 2,3-dichloro-1-propanol as described in any one of 1) to 4) above, wherein the chlorination reaction of allyl alcohol is performed at a pressure of 1 MPa (gauge pressure) or less.
8) A method for producing epichlorohydrin, characterized in that the method comprises subjecting 2,3-dichloro-1-propanol as produced in any one of 1) to 7) above to saponification reaction.